Dispersion Of Graphene Oxide Sheets Research Articles

Stabilization of lysozyme in aqueous dispersion of graphene oxide sheets

This study examines the effect of surface oxygen groups upon ability of graphene oxide (GO) sheets in suppressing the fibrillation of lysozyme (LYZ). Graphite was oxidized using 6 and 8 wt equivalents of KMnO4, and as produced sheets were abbreviated as GO-06 and GO-08, respectively. Particulate characteristics of sheets were characterized by light scattering and electron microscopic techniques, and their interaction with LYZ was analysed by circular dichroism (CD) spectroscopy. After ascertaining acid-driven conversion of LYZ to fibrillary form, we have shown that the fibrillation of dispersed protein can be prevented by adding GO sheets. Inhibitory effect could be attributed to binding of LYZ over the sheets via noncovalent forces. A comparison between GO-06 and GO-08 samples showed superior binding affinity of the latter. Higher aqueous dispersibility and density of oxygenated groups in GO-08 sheets would have facilitated the adsorption of protein molecules, thus making them unavailable for aggregation. Pre-treatment of GO sheets with Pluronic 103 (P103, a nonionic triblock copolymer), caused reduction in the adsorption of LYZ. P103 aggregates would have rendered the sheet surface unavailable for the adsorption of LYZ. Based on these observations, we conclude that fibrillation of LYZ can be prevented in association with graphene oxide sheets.

Efficient Use of Graphene Oxide and Silica Fume in Cement-Based Composites.

Incorporation of graphene oxide (GO) and silica fume (SF) to cement composites enhances their mechanical properties if suitable proportional amounts of GO and SF are used. This study presents a simplified approach to determine experimentally the optimum GO and SF contents that should be added to the cementitious mixture to obtain a proper and stable dispersion of GO sheets within the cement matrix. Composite mortar specimens with different GO and SF contents were designed and tested under flexural and compression loading. The phase formation and the microstructure of selected samples were also investigated to give an in-depth interpretation of the test results. The main criterion to determine the GO and SF contents was the ultimate strength required of the GO–cement composite. It was found that there was a composite interaction between the SF and GO contents in the cementitious mixture, which an envelope surface could describe if all other mix design parameters are kept constant.

Graphene nanoplatelets can improve the performances of graphene oxide – polyaniline composite gas sensing aerogels

Aerogels are commonly regarded as soft and versatile materials for multiple applications thanks to their features such as elastic behavior, swelling ability and responsive characteristics. In the last decades these qualities have ensured them multiple uses in biomedical field as controlled drug delivery systems and scaffolds for tissue engineering applications. Recently their employment as sensors has attracted great interest especially thanks to their tunability and the possibility to be used as soft material instead of conventional and many times unreliable sensors in multiple sensing applications. In this work we synthetized graphene oxide/polyaniline aerogels by in situ chemical polymerization of aniline monomer in aqueous dispersion of graphene oxide sheets. We characterized the system through chemical and mechanical analysis, and we its responsivity as gas sensing device was verified. Moreover, we investigated the influence of the encapsulation of graphene nanoplatelets on the responsive ability of the device. The addition of the graphene moieties improves the conductivity of the system, its compressive mechanical resistance and the applicability of these devices as gas sensors.

Incorporation of silica network and modified graphene oxide into epoxy resin for improving thermal and anticorrosion properties

AbstractIn this study, the silica network and functionalized graphene oxide (GO) were incorporated into the epoxy coating systems, which was aimed to improve the thermal property and corrosion resistance of epoxy coatings. First, tetraethyl orthosilicate (TEOS) oligomers and epoxy hybrid was fabricated through sol–gel method. Then the (3‐aminopropyl) triethoxysilane (APTES) modified graphene oxide (FGO) was added into the epoxy hybrid composite to obtain anticorrosion coatings. Fourier transform infrared spectroscopy, thermogravimetric analysis (TGA), Raman spectrum, and X‐ray photoelectron spectrum were conducted to evaluate the structural information of GO and APTES modified GO nanosheets. The results indicated that the APTES successfully grafted onto the surface of GO sheets. Besides, TGA curves, electrochemical measurements and salt spray test were also carried out to characterize the thermal performance and corrosion resistance of GO based epoxy coatings. The TGA results revealed that the thermal performance of epoxy coating containing silica network and FGO nanofiller (ES/FGO) was significantly strengthened compared to pure epoxy. The initial degradation temperature of epoxy coating was increased from 300 to 343.7°C after incorporation of silica component and FGO. The EIS measurements demonstrated that the impedance modulus of ES/FGO was significantly higher than neat epoxy, which indicated that the corrosion resistance of epoxy was substantially strengthened after introduction of silica component and FGO. The corrosion rate and inhibition efficiency of epoxy composite coatings were also shifted from 1.237 × 10−7 mm/year and 76.6% (for neat epoxy) to 1.870 × 10−9 mm/year and 99.6% (for ES/FGO), respectively. The salt spray test also revealed that the silica and FGO can improve the corrosion resistance of epoxy coating. Additionally, the dispersion of GO sheets was also enhanced after the modification of APTES siloxane.

A novel approach to fabricate polyacrylate modified graphene oxide for improving the corrosion resistance of epoxy coatings

In the past decades, graphene oxide (GO) exhibited great potential for enhancing the performance of polymer composites. Homogeneous dispersion of GO sheets in the polymer matrix was still a main challenge for the application of GO materials. In this paper, the polyacrylate functionalized GO (PA-GO) was prepared through free-radical copolymerization technology, with the aim to enhance the dispersion of GO in epoxy coatings. Fourier transform infrared (FT-IR), 1H-nuclear magnetic resonance spectroscopy (1H-NMR), Raman, thermogravimetric analysis (TGA), scanning electron microscope (SEM) and transmission electron microscope (TEM) were conducted to inspect the structure and micromorphology of GO and PA-GO nanosheets. The results affirmed that the polyacrylate polymer has successfully grafted onto graphene oxide. The SEM results revealed that the GO nanoplatelets exhibited significantly improvement in the dispersion and interfacial interaction in the epoxy matrix after modification with polyacrylate polymer. Electrochemical measurements were also employed to evaluate the corrosion resistance of GO-based epoxy composite coatings. The EIS results indicated that the impedance modulus at low frequency (0.01 Hz) of epoxy coating containing PA-GO was increased by almost two orders of magnitude compared to the neat epoxy, demonstrating that the corrosion resistance of epoxy coating was significantly improved after introduction of PA-GO. Besides, the Tafel results showed that the corrosion rate of epoxy coating was also decreased from 4.814 × 10−7 mm/year to 1.701 × 10−8 mm/year, which also indicated that the incorporation of PA-GO effectively strengthened the corrosion protection performance of epoxy coating.

Green Solvent Processed Cellulose/Graphene Oxide Nanocomposite Films with Superior Mechanical, Thermal, and Ultraviolet Shielding Properties.

This study reports for the first time a green process to fabricate Lyocell fiber and graphene oxide (GO) based novel cellulose/graphene oxide nanocomposite (CGN) flexible films for ultraviolet (UV) shielding applications. A polyethelene glycol (PEG) mediated solvent system was utilized to make CGN films via solution casting route. To improve the dispersion of GO sheets in a cellulosic matrix, a reactive interface was formed in between cellulose and oxygenic functionalized groups of GO sheets via cross-linking them with epichlorohydrin (ECH). The addition of GO sheets in cellulose matrix leads to the synergistic changes, which were observed in the structure and surface morphology of CGN nanocomposite films. Enhanced dispersion of GO sheets in CGN films was observed in morphological investigations which is attributed to the adequate cellulose-GO interaction by hydrogen bonding and led to significant enhancement in the mechanical and thermal properties. The tensile strength and Young's modulus of CGN films with 2 wt % GO loading (CGN2) increased to 89 MPa and 4.3 GPa from 55.6 MPa and 2.1 GPa, respectively, as compared to the neat cellulosic film. Additionally, the CGN films exhibited remarkable UV shielding capability which increased with GO loading in a cellulose matrix. The CGN2 film (2 wt % GO loading) possessed outstanding absorbance in the wavelength range of 280 to 400 nm and showed almost complete shielding (∼99%) of UV rays in both the UV-B and the UV-A regions. Moreover, the ultraviolet protection factor of the CGN2 film demonstrated more than 80-fold increase compared to that of the neat cellulose film. The obtained CGN nanocomposite film has a high potential for applications in the field of UV protection.

Corrosion resistance of copolymerization of acrylamide and acrylic acid grafted graphene oxide composite coating on magnesium alloy

Acrylamide (AM)/acrylic acid (AA) functionalized graphene oxide (GO) composites (GMAs) were readily prepared by one-step copolymerization and coated on the surface of magnesium alloy. Ultraviolet–visible spectroscopy (UV–vis), Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS), and Raman results provided the evidences of the successfully polymerization of AM/AA on the surface of GO nanosheets. Thermogravimetric analysis (TGA) revealed the grafting amount of polymer to GO. X-ray diffraction (XRD) patterns showed that d-spacing of GO nanosheets increased with insertion of polymer chains. The morphologies of GMAs and dispersibilities of GO in aqueous solution were investigated by field emission scanning electron microscopy (FESEM) and transmission electron microscope (TEM), which showed a polymeric layer covered the surface of GO sheets. The excellent dispersion of GO sheets in a polymer matrix can significantly enhance the corrosion protection effect for a metal substrate because the GO sheets played a role of the physical barriers and some polar groups in coatings could intercept corrosive ions. The developed one-step copolymerization method was facile, rapid and the fabricated GMAs showed potential for application as corrosion resistance coatings.

Design and mechanistic understanding of graphene oxide reinforced zein nanocomposites with improved mechanical, barrier and thermal properties

Graphene oxide (GO)-based zein nanocomposite films with superior mechanical, barrier and thermal properties were fabricated by incorporating GO nanoparticles into corn protein zein (Z), through the solvent casting process. The study offers a mechanistic understanding of the effect of graphene oxide nanofiller on the physicochemical properties of zein. TEM of the zein–graphene oxide (Z–GO) nanocomposites showed uniform dispersion of GO sheets up to 1%GO loading. Mechanisms for Z–GO nanocomposite formation through covalent and noncovalent bonding are developed based on FTIR, FT-Raman and DSC results. At only 3% loading, the Young’s modulus of a nanocomposite film increased by 300% and tensile strength increased by 80%. The increases in mechanical property improvements are accompanied by surface roughness increases as indicated by AFM studies. Even though GO is hydrophilic, the Z–GO nanocomposite films showed hydrophobic tendencies. The amount and degree of exfoliation of GO as well as the relative orientation of GO nanoparticles within the zein film all play an important role in the physical property changes of the film. The films became less permeable with increasing amounts of GO addition, as shown by water vapor permeability tests. GO increased thermal stability as shown by TGA.

Synthesis and characterization of hybrid materials based on graphene oxide and silica nanoparticles and their effect on the corrosion protection properties of epoxy resin coatings

This study focuses on the use of tetraethyl orthosilicate (TEOS) as a silica source to decorate the surface of graphene oxide (GO) nanosheets and the use of N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane (Z-6020) as a coupling agent through a one-step in-situ sol-gel process. The results of the Fourier transform infrared spectroscopy (FT-IR), UV-visible, X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA) revealed that fine SiO2 nanoparticles have successfully been synthesized on the basal plane of GO by covalent bonding. The dispersion of GO sheets and GO–SiO2 nanohybrids within the epoxy matrix was studied using XRD and SEM techniques. Then, the effect of incorporating 0.1 wt% GO sheets and GO–SiO2 nanohybrids on the corrosion protection and barrier performance of the epoxy coating was also investigated. The results showed that the incorporation of GO–SiO2 into the epoxy matrix improved its thermal stability. The electrochemical impedance spectroscopy (EIS) test, potentiodynamic polarization and cathodic disbonding test showed that the corrosion protection performance was significantly enhanced by the incorporation of GO–SiO2 hybrids into the epoxy resin compared to epoxy/GO and neat epoxy resin, respectively. The water contact angle (CA) results confirmed the reduction of the hydrophobic nature of the surface after the incorporation of GO–SiO2 hybrids.

Failure behaviour of an epoxy coating with polyaniline modified graphene oxide under marine alternating hydrostatic pressure

Polyaniline (PANI) was used to modify the graphene oxide (GO) by in-situ polymerization. The failure behaviour of epoxy resin-based GO-PANI coating under marine alternating hydrostatic pressure (AHP) was investigated. The results indicated that PANI modification improves the dispersion of GO sheets and reduces the formation of initial surface defects, both of which significantly increase the compactness and mechanical properties of the coating. The improvement of the pigments/binder interface retards the diffusion of electrolyte and the deterioration of coating structure caused by AHP. The excellent anti-permeability of coating not only depends on the improvement of compatibility between GO and binder, but also the superior toughness provided by GO-PANI nanosheets.

Controlled quercetin release from high-capacity-loading hyperbranched polyglycerol-functionalized graphene oxide.

PurposeAn efficient drug-delivery system was prepared based on graphene oxide using a facile and one-step strategy for controlling the release of anticancer drugs.MethodsFabrication of single-layer graphene oxide (GO) sheets was carried out by both modified and improved Hummers method. Biocompatible hyperbranched polyglycerol (HPG) was grafted on the surface of GO through the ring-opening hyperbranched polymerization of glycidol. Various ratios of GO and glycidol were used for polymer grafting. An anticancer drug, quercetin (Qu), was loaded into modified GO via noncovalent interactions.ResultsPolymer grafting on the surface of GO sheets was confirmed by results obtained from Fourier-transform infrared and Raman spectroscopy, thermogravimetric analysis, energy-dispersive X-ray and X-ray spectroscopy, scanning electron microscopy, and atomic force microscopy. It was revealed that polymerization increased d-spacing between the basal planes. In addition, as a hydrophilic polymer, HPG improved the stability and dispersion of GO sheets in biological solutions and endowed extra drug-loading capacity for the sheets. The effect of hyperbranched structure on drug loading and release was investigated by comparing drug loading and release for HPG-modified GO and linear PPO-modified GO. Our experiments indicated high drug-loading capacity (up to 185%), and excellent encapsulation efficiency (up to 93%) for HPG-GO compared to linear PO-grafted GO. The release profile of Qu under various pH levels exhibited controlled and sustained drug release without an initial burst effect for HPG-GO, suggesting that an acidic solution could facilitate drug release. HPG-GO did not show any cytotoxicity on the MCF7 cell line in different concentrations during 72 hours’ incubation. Uptake and entrance of HPG-GO into the cells were verified by determining the intracellular amount of Qu by high-performance liquid chromatography.ConclusionA combination of the unique properties of GO and the biodegradable polymer polyglycerol revealed high drug-loading capacity, pH-dependent drug release, and cytocompatibility with HPG-GO, thus introducing it as a promising nanocarrier for anticancer drug delivery.

Adsorption and determination of polycyclic aromatic hydrocarbons in water through the aggregation of graphene oxide

Abstract In this study, a simple method was developed for the aggregation of graphene oxide (GO) with the addition of NaCl to concentrate and separate polycyclic aromatic hydrocarbons (PAHs) from water samples, and this method was used as a environmentally friendly method for the determination of PAHs. We demonstrate the uniform dispersion of GO sheets in aqueous samples for the fast high-efficiency adsorption of PAHs. Aggregation occurred immediately upon elimination of electrostatic repulsion by adding NaCl to neutralize the excessive negative charges on the surfaces of the GO sheets. The aggregates of GO and PAHs were separated and treated with hexane to form a slurry. The slurry was filtered and subjected to gas chromatography–mass spectroscopy (GC-MS) analysis. Based on a 40-mL sample volume, limits of detection of 10–30 ng L-1 were obtained for 16 PAHs, with correlation coefficients (R2) exceeding 0.99. The method yielded good recovery, ranging from 80 to 111% and 80 to 107% for real spiked water samples at 100 and 500 ng L-1, respectively. Compared to traditional solid-phase extraction and liquid–liquid extraction methods, this method is free of organic reagents in the pretreatment procedure and uses only 1 mL hexane for sample introduction.

Graphene Oxide as An Efficient Photocatalyst For Photocatalytic Reduction of CO2 Into Solar Fuel

Photocatalytic reduction of CO2 into solar fuel such as methane and methanol, is an attractive approach to simultaneously solve the energy crisis and global warming problem. Herein, comparative photocatalytic activity of graphene oxide nanosheets have been investigated for photocatalytic reduction of CO2 into methane and methanol in continuous gas and liquid phase photoreactor system. The graphene oxide sheets were prepared according to Tour's method. The chemical composition and optical properties was evaluated through XPS and UV-vis spectroscopy. Graphene oxide nanosheets exhibited maximum amount of 224.87 I¼mol/g.h methanol and 14.8 I¼mol/g.h methane in liquid and gas phase system, respectively. Higher yield of methanol in liquid phase compared to methane in gaseous system can be attributed to dispersion of graphene oxide sheets in water. Hence, graphene oxide nanosheets are efficient photocatalyst for CO2 reduction into methanol. Nevertheless, further research is essential to improve the photostability of graphene oxide sheets for real application of photocatalytic CO2 reduction. © Universiti Malaysia Pahang, Malaysia.

Surfactant-free electrodeposition of reduced graphene oxide/copper composite coatings with enhanced wear resistance

Abstract How to uniformly disperse graphene sheets into the electrolyte is one of the main challenges to synthesize graphene enhanced nanocomposites by electrodeposition. A surfactant-free colloidal solution comprised of copper (II)-ethylene diamine tetra acetic acid ([CuIIEDTA]2−) complexes and graphene oxide (GO) sheets is proposed to electrodeposit reduced graphene oxide/copper (RGO/Cu) composite coatings. Anionic [CuIIEDTA]2− complexes stably coexist with negatively charged GO sheets due to the electrostatic repulsion between them, facilitating the electrochemical reduction and uniform dispersion of GO sheets into the copper matrix. The RGO/Cu composite coatings are well characterized by XRD, Raman, SEM and XPS. Their tribological behavior as a function of RGO content in composite coatings and normal loads are investigated. Also the chemical composition and topography of the wear tracks for the composite coatings are analyzed to deduce the lubricating and anti-wear mechanism of RGO/Cu composite coatings.

Synthesis and characterization of GO-hydrogels composites

The preparation of poly(N-isopropylacrylamide) (PNIPAm) hydrogel nanocomposites containing graphene oxide (GO) and GO plus carbon nanotubes (CNT) in the polymer network is communicated. This one-pot preparation methods include the dispersion of GO (or GO plus CNT) in a solution of monomers and the subsequent polymerization. The texture of the nanocomposites was studied using scanning electron microscopy (SEM), where very compact surfaces are observed suggesting good dispersion of GO sheets and CNTs within the polymer matrix. The presence of GO inside the polymer network diminished the equilibrium swelling values and increased the elastic modulus up to 162 % with respect to the pure gel. Similar results were observed for the composite with CNT. Furthermore, the electrical resistivity of PNIPAm-GO diminishes as the applied compression force increases, being 50 % lower than hydrogel without GO. Moreover, the electrochemical properties of the hydrogels, evaluated by cyclic voltammetry, indicate highly reversible electrical charge/discharge response. In order to apply these materials for antibiotic delivery, the absorption of tetracycline (tet) is evaluated and the nanocomposites showed better absorption capability and improved antibiotic delivery. Preliminary results suggest that tet loaded PNIPAm-GO and PNIPAM-GO-CNT display antimicrobial activity against the Pseudomonas aeruginosa turning these materials as potential candidates for biomedical applications.

High temperature ablation and thermo-physical properties improvement of carbon fiber reinforced composite using graphene oxide nanopowder

Ablative nanocomposites were prepared by incorporating graphene oxide (GO) nanosheets into resole type phenolic resin and then impregnating them into rayon-based carbon fabric. GO were dispersed into phenolic resin at 0.25, 0.75, and 1.25wt.% loadings using high shear mixing to insure uniform GO dispersion. The morphology and structure of graphene oxide nanosheets (synthesized by a Hummers method) and the structural, thermal and ablative properties of the samples were characterized using Fourier Transform Infrared spectroscopy(FTIR), X-ray Diffraction (XRD), Scanning Electron Microscope (SEM), oxyacetylene flame test, and Thermo-Gravimetric Analysis (TGA) methods. It was found that the thermal stability and ablative properties of the GO/phenolic resin/carbon fiber composites were greatly enhanced due to the well dispersion of GO sheets in polymer matrix and the strong interfacial interaction between the GO sheets and phenolic matrix as well as layered carbon structure after pyrolysis. The specimen with 1.25wt.% GO showed the best results in the rate of ablation, thermal diffusivity and thermal stability compared to other samples. This laminate had constant thermal diffusivity at different temperatures, and improved char yield and ablation rate to about 10% and 51%, respectively.

Electrical and mechanical properties of poly(dopamine)-modified copper/reduced graphene oxide composites

Surface oxidation is frequently encountered in powder metallurgy of metals and alloys, and it leads to a reduction in their electrical conductivities. Therefore, it is highly desired to remove the naturally occurring oxide layer from the particles surface and to prevent its subsequent formation. A new approach was proposed in this study, where copper particles were mixed with graphene oxide (GO) sheets in an aqueous solution containing dopamine (DA) molecules. It was expected that polymerization of the DA molecules on the surface of the copper particle could promote both a reduction of surface oxide layer and the adhesion of GO sheets to the particles surface. The powder system was then washed, heat-treated in inert atmosphere and compressed at room temperature to form compacts. Electron microscopy revealed nearly ideal dispersion of GO sheets within the copper matrix. X-ray photoelectron spectroscopy showed a shift from Cu2+ to Cu+ and metallic copper in the coated and heat-treated samples, and Raman spectroscopy pointed to the increased amount of sp 2 carbon as a result of the heat treatment. All DA/GO-coated and heat-treated compacts exhibited significantly higher electrical conductivity than those that have been made from pure copper powder or were not been heat-treated. Also, indentation measurements showed an increase in microhardness in samples with the shortest, 10 min, coating time and heat-treated at the highest, 600 °C, temperature.

Enhanced thermo‐physical properties of nitrile‐butadiene rubber nanocomposites filled with simultaneously reduced and functionalized graphene oxide

3‐Mercaptopropyltrimethoxysilane (MPTMS) modified exfoliated graphene oxide (GO)/nitrile‐butadiene rubber (NBR) nanocomposites were fabricated by latex compounding method. The modification and reduction of GO were simultaneously conducted in situ by a one‐pot design. The reductant, ammonium hydroxide was employed to mildly reduce GO at 78°C. The GO exfoliation, MPTMS modified GO (MGO), and the dispersion of GO sheets in rubber matrix were studied using Wide‐angle X‐ray diffraction (XRD), Fourier transformation infrared spectroscopy (FT‐IR), and transmission electron microscopy (TEM). It is evident that GO sheets are uniformly dispersed in the rubber matrix. The one‐pot design can significantly promote the reduction process and the surface modification of GO, simultaneously. The reduction was confirmed by morphology analysis and FT‐IR analysis of uncured rubber compounds. The mechanical properties of pristine NBR/GO and NBR/MGO nanocomposites were studied within a filler range of 0–2 phr. The NBR/MGO composites exhibited superior mechanical property and higher storage modulus attributing to the stronger interfacial interaction via covalent bonding between MGO and NBR molecules compared with the NBR/GO composites connected by weaker π–π stacking. POLYM. COMPOS., 39:3227–3235, 2018. © 2017 Society of Plastics Engineers

One-pot in situ polymerization of graphene oxide nanosheets and poly(p-phenylenebenzobisoxazole) with enhanced mechanical and thermal properties

Graphene with unique nanostructures possess fascinating properties which has inspired extensive research on the incorporation of graphene into polymer matrix to improve the properties. So, in this report, we take a facile and effective approach, one-pot in situ polymerization, to prepare graphene oxide (GO)/Poly(p-phenylene benzobisoxazole) (PBO) composite fibers. The GO sheets were first modified by 4, 6-diaminoresorcinol (DAR) a PBO monomer, another monomer terephthalic acid (TPA) were then added for further polymerization. The NH2-functionalized GO (DAR-GO) sheets are an excellent initial platform for molecular chains grafting. It promote the dispersion of GO sheets in PBO matrix and form strong interaction with the PBO molecular chains to enhance load transfer. The tensile module and tensile strength of the PBO-DAR-GO composite fibers containing 1.0 wt% DAR-GO are increased by 35.9% and 19.6%, respectively compared with neat PBO fibers. In addition, the thermal stability of composite fibers also enhanced with DAR-GO content increasing. This approach supplies a novel strategy for preparing ultra-strong properties PBO composite fibers.

Thermally induced all-optical inverter and dynamic hysteresis loops in graphene oxide dispersions.

We experimentally study the temporal dynamics of amplitude-modulated laser beams propagating through a water dispersion of graphene oxide sheets in a fiber-to-fiber U-bench. Nonlinear refraction induced in the sample by thermal effects leads to both phase reversing of the transmitted signals and dynamic hysteresis in the input-output power curves. A theoretical model including beam propagation and thermal lensing dynamics reproduces the experimental findings.